fix: resolve kmp-sdk build failure on iOS native test compilation

Replace assert() with assertTrue() in MrzKeyUtilsTest to avoid
ExperimentalNativeApi opt-in requirement on Kotlin/Native. Also
gitignore the copyWebViewAssets build artifact (shared/src/main/).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/kmp-sdk/.gitignore

@@ -8,3 +8,4 @@ build/
 *.log
 *.tmp
 local.properties
+shared/src/main/

packages/kmp-sdk/shared/src/commonTest/kotlin/xyz/self/sdk/models/MrzKeyUtilsTest.kt

@@ -49,7 +49,7 @@ class MrzKeyUtilsTest {
     fun computeMrzKey_pads_short_passport_number() {
         val key = MrzKeyUtils.computeMrzKey("AB1234", "900101", "300101")
         // "AB1234" padded to 9 → "AB1234<<<"
-        assert(key.startsWith("AB1234<<<"))
+        assertTrue(key.startsWith("AB1234<<<"))
         assertEquals(24, key.length)
     }